Interpretive Summary: The emerald ash borer (EAB) has now become a devastating forest pest in North America, killing hundreds of millions of native North American ash (Fraxinus spp.) trees since its discovery in
Michigan, USA in 2002. A new species of parasitic wasp (Spathius galinae) was recently discovered in the Russian Far East, and has now been imported to the USDA quarantine facility at Newark, DE for consideration for release against EAB in the north central and northeastern United States. Because this new parasitic wasp attacks the same larval stages of EAB as the previously introduced Chinese parasitic wasp (Tetrastichus planipennisi), however, the
potential exists for competition between these two parasitoids and their competitive interactions need to be investigated before deciding whether or not to release the new Russian parasitic wasp in the United States. We conducted laboratory experiment to examine the potential interactions between these two parasitic wasps when they compete for the same EAB host larvae. Results from our study showed that the new Russian parasitic wasp (S. galinae)
attacked EAB larvae already parasitized by the previously introduced Chinese parasitic wasp (T. planipennisi) for up to 4 days, but not 8 days. However, parasitism rates were significantly
lower in previously parasitized hosts as compared to healthy EAB larvae. These results suggest that potential negative effects, if any, of releasing the Russian parasitic wasp on the current
EAB biocontrol program involving introduction of the Chinese parasitic wasp may be greatly reduced by the ability of the Russian parasitic wasp to discriminate healthy EAB larvae from
hosts previously parasitized by other species of larval parasitoids.

Technical Abstract:
Understanding interspecific competition among insect parasitoids is important in designing classical biological control programs that involve multiple species introductions. Spathius galinae, a new idiobiont ectoparasitoid from the Russian Far East, is currently being considered for introduction to the United States for biological control of the emerald ash borer, Agrilus planipennis (EAB), whereas Tetrastichus planipennisi, a koinoboint
endoparasitoid native to China, is another natural enemy that has already been introduced in the same program. In a laboratory study, we examined the potential interactions between these
two parasitoids when they compete for the same EAB host larvae. In multiple-choice assays where healthy EAB larvae were presented along with EAB larvae previously parasitized by T. planipennisi at different times, we found S. galinae attacked EAB larvae already parasitized by T. planipennisi for up to 4 days, but not 8 days. However, parasitism rates were significantly lower in previously parasitized hosts as compared to healthy EAB larvae. In no-choice tests where S. galinae females were presented either with healthy EAB larvae or EAB larvae parasitized by T. planipennisi at several earlier time points, S. galinae again parasitized significantly more healthy EAB larvae than T. planipennisi-parasitized larvae. These results suggest that the ectoparasitoid S. galinae can discriminate between healthy host larvae and T. planipennisi-parasitized larvae. Relevance of those findings to the current EAB biocontrol program that involves introduction and releases of multiple species of larval parasitoids is discussed.